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LibWeb: Respect CSS z-index property while painting

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To support z-ordering when painting, the layout tree now has a parallel
sparse tree of stacking contexts. The rules for which layout boxes
establish a stacking context are a bit complex, but the intent is to
encapsulate the decision making into establishes_stacking_context().

When we paint, we start from the ICB (LayoutDocument) who always has a
StackingContext and then paint the tree of StackingContexts where each
node has its children sorted by z-index.

This is pretty crude, but gets the basic job done. Note that this does
not yet support hit testing; hit testing is still done using a naive
treewalk from the root.
This commit is contained in:
Andreas Kling 2020-06-15 17:29:35 +02:00
parent ce3260c6bf
commit 96da15a8a4
11 changed files with 222 additions and 3 deletions
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8
Libraries/LibWeb/CSS/StyleProperties.cpp
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@ -185,6 +185,14 @@ float StyleProperties::line_height(const LayoutNode& layout_node) const
return (float)font().glyph_height() * 1.4f;
}
Optional<int> StyleProperties::z_index() const
{
auto value = property(CSS::PropertyID::ZIndex);
if (!value.has_value())
return {};
return static_cast<int>(value.value()->to_length().raw_value());
}
CSS::Position StyleProperties::position() const
{
if (property(CSS::PropertyID::Position).has_value()) {